EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

Refractory complex concentrated alloys (RCCAs) are potential substitutes for nickel or TiAl alloys for high temperature application in aircraft engines, between 800°C and 1000°C. In particular, the Ti- Nb-Al ternary system with the precipitation of stable orthorhombic phase in the bcc matrix shows good mechanical properties both at both room (with good ductility) and high temperatures (with high resistance), but its use is limited above 800°C. In order to increase the service temperature of such alloys the effects of the substitution of Nb by Ta (0 to 25 at%) and of Al by Si (1 at%) on the microstructure and mechanical properties have been investigated. On the one hand, if the addition of Ta does not modify the O-phase precipitates morphology, two populations can be distinguished by their crystal structure. One remains orthorhombic whereas the second one exhibits a very similar crystal structure but with a hexagonal symmetry corresponding to the well-known α2 phase. On the second hand, addition of Si leads to, in addition to the O-phase plates, the precipitation of very thin needles of δ–Nb11Si4 silicides identified for the first time in this system.
The evolution of the mechanical properties with the chemical composition and heat treatments has been followed by hardness measurements and compression tests at 800°C, and discussed in relation with the observed microstructures.